1. Field of the Invention
The present invention relates to a content transfer system, a content transfer method, a content transmitting apparatus, a content transmission method, a content receiving apparatus, a content reception method, and a computer program for which a transmitting apparatus transfers content to a plurality of receiving apparatuses, in particular, those for which a server that stores content such as audio and visual data effectively transfers the content to clients in accordance with their requests.
In more detail, the present invention relates to a content transfer system, a content transfer method, a content transmitting apparatus, a content transmission method, a content receiving apparatus, a content reception method, and a computer program for which content is effectively transferred from a server to a plurality of clients so that the content is restricted for private use. In particular, the present invention relates to a content transfer system, a content transfer method, a content transmitting apparatus, a content transmission method, a content receiving apparatus, a content reception method, and a computer program for which content is effectively transferred from a server to a plurality of clients in accordance with the provision of Digital Transmission Content Protection (DTCP).
2. Description of Related Art
It is known that when a plurality of computers are mutually connected to a network, information and hardware resources are shared and collaborated by a plurality of users. There are a variety of media that connect computers, such as Local Area Network (LAN), Wide Area Network (WAN), and Internet.
Recently, circulation and distribution services for content such as video and music data through networks have been widespread. These sorts of services do not need to move media such as CDs and DVDs. In addition, a content distribution request equivalent to purchase of a medium can be remotely issued through a network. Content can be obtained by a simple process at low cost and almost in real time without need to deliver a medium.
However, content that is handled through networks are digital data that can be illegally manipulated, for example, copied and falsified, relatively with ease. Presently, illegal acts such as copy and falsification of digital content are being frequently performed. They are becoming a major factor that disturbs profit of digital content vendors. Thus, a vicious cycle of which a price of content is increased and digital content is prevented from being widespread has occurred.
Under the provision of the copyright law, digital content is protected against illegal uses such as copy without permission of the copyright owner and falsification of content. Article 30 of Japanese Copyright Law states that “It shall be permissible for a user to reproduce by himself a work forming the subject matter of copyright (hereinafter referred to as a “work”) for the purpose of his personal use, family use or other similar uses within a limited circle (hereinafter referred to as “private use”), except . . . ” In addition, Article 49 (1) states that if a user has produced a copy of the work for private use, when he uses the copy not for private, his act shall be considered to constitute the reproduction, namely this article prohibits the user from using the copied work not for private.
Nowadays, digital contents have been widely used and many techniques that protect copyright thereof have been developed. The DTCP, which is the industry standard, prescribes a scheme for which content is transmitted while its copyright is protected, for example, a communication range in which content is transferred and the number of devices that receive the content are restricted (for example, refer to Non Patent Document 1).
Originally, the DTCP prescribes transfer of digital content through a home network that uses IEEE 1394 or the like as a transfer path. Transfer of content through a home network is considered to be personal use or home use in the Copyright Law. The DTCP prescribes an authentication protocol for devices during a content transfer and a transfer protocol for encrypted content. In other words, a server that is a content provider authenticates a client that is a content recipient. The server encrypts a transfer path using a key shared by the server and the client through the authentication process and transfers the content to the client. Thus, in the DTCP, content can be transferred while it is protected. In addition, unless the client has been successfully authenticated with the server, since the client cannot obtain an encryption key, the client cannot enjoy the content.
In addition, recently, a technique of which the DTCP based on the IEEE 1394 is implemented to the IP network has been developed (hereinafter, this technique is referred to as the DTCP-IP). Many of home networks are connected to an external broadband network such as the Internet through a router or the like. Thus, with the establishment of the DTCP-IP technique, while digital content is protected, the content can be more flexibly and effectively used than the IP networks.
The DTCP-IP is a technique of which the DTCP is implemented to the IP network and adopted in the DTCP specification. However, in the DTCP-IP, the IP network is used as a transfer path and encrypted content is transferred in accordance with the HTTP or RTP protocol. Thus, in these points, the DTCP-IP is different from the DTCP based on the IEEE 1394 (as was described above). Various devices that are mainly PCs are connected through the IP network. Thus, data can be easily wiretapped and falsified, the DTCP-IP further prescribes another method for which content is transferred through a network while the content is protected (for example, refer to Non Patent Document 2).
Next, a transfer process for contents in accordance with the DTCP-IP will be described. DTCP compliant devices are categorized as two types. The first type is referred to as a DTCP_Source that is a server device that receives a request for content and transmits the content. The second type is a DTCP_Sink that is a client device that requests content, receives the content, and reproduces or records the content.
The DTCP_Source and the DTCP_Sink establish one TCP/IP connection and authenticate each other. This authentication is referred to as the DTCP authentication or the authentication and key exchange (AKE). In a DTCP compliant device, a unique device ID and a key have been embedded by a licensing organization called Digital Transmission Licensing Administrator (DTLA). In the DTCP authentication process, with these embedded information, after they have checked that they are right DTCP compliant devices, they can share a key to encrypt or decrypt content, which the DTCP_Source manages, with a DTCP_Sink device.
After the DTCP compliant devices have authenticated each other, the DTCP_Sink requests content from the DTCP_Source. The DTCP_Source can inform the DTCP_Sinc of a content location that represents the access destination of the content of the DTCP_Source through Content Directory Service (CDS) or the like in advance. When the DTCP_Sinc requests content from the DTCP_Source, the DTCP_Sinc can use a protocol such as the hyper text transfer protocol (HTTP) or the real time protocol (RTP). When the DTCP_Sinc requests content from the DTCP_Source in accordance with the HTTP, the DTCP_Source becomes an HTTP server and the DTCP_Sinc becomes an HTTP client. The HTTP server starts transferring the content to the HTTP client. When the DTCP_Sinc requests a content from the DTCP_Source in accordance with the RTP, the DTCP_Source becomes an RTP sender and the DTCP_Sinc becomes an RTP receiver. The RTP sender starts transferring the content to the RTP receiver. Besides these communication protocols, other protocols such as real time streaming protocol (RTSP) may be used.
When content is transferred in accordance with the HTTP, the HTTP client establishes a TCP/IP connection in accordance with the HTTP in addition to the TCP/IP connection for the DTCP authentication. The HTTP client requests content from the HTTP server in accordance with the same process as the regular HTTP. The HTTP server returns the requested content as an HTTP response to the HTTP client. Data transferred as the HTTP response are data of which content is encrypted with a key shared after the HTTP server, namely the DTCP_Source device, has AKE authenticated the HTTP client. The client device (DTCP_Sinc) that has received encrypted data decrypts data with the key shared after the client device has been authenticated and reproduces or records the decrypted data.
As described above, the DTCP-IP provides a safe content transfer method that prevents content from being wiretapped or falsified through a transfer path in the manner that DTCP compliant devices are authenticated by each other, a key is shared by the devices that have been DTCP authenticated by each other, and content to be transferred is encrypted and decrypted.    [Non Patent Document 1] DTCP Specification Volume 1 Version 1.3 (Informational Version).    [Non Patent Document 2] DTCP Volume 1 Supplement E Mapping DTCP to IP, Version 1.0 (Informational Version).